Electrical signal lines are commonly used nowadays to connect and transfer electrical signals between different electrical or electronic appliances. Due to the presence of the environmental electromagnetic field, electrical noises are very easy induced in the signal lines which deteriorates the quality of signal transferring and consequently negatively affects the performance of the electrical or electronic appliances.
To overcome the problem of electrical noise induced by the surrounding electromagnetic field, there are noise filtering devices available in the market. An example of the currently available noise filtering devices is shown in FIGS. 7 and 8 of the accompanying drawings. As shown, the currently available noise filtering device, which is designated by the reference A in FIGS. 7 and 8, generally comprises a casing constituted by two members B and C which are connected by thin and flexible connections D so as to be rotatable relative to each other and thus openable. Each of the casing members B and C has a recess into which a magnet 1A is disposed.
The magnets 1A have a groove 1B formed thereon to allow signal wire of which the electrical noise induced thereon by surrounding electromagnetic field is to be eliminated by the noise filtering device A to extend therethrough.
The conventional noise filtering device, however, has disadvantages. Some of the disadvantages are:
(1) The casing members B and C are secured together, when closed, by hooks and slots formed thereon, which hooks and slots are basically weak members and require manufacturing precision and thus causing manufacturing difficulty. PA1 (2) The magnets 1A are simply disposed in the recesses formed on the casing members B and C without any retaining means so that due to the manufacturing tolerance of casing members B and C, the magnets 1A may be easy to disengage from the casing members B and C and thus causing an inconvenience to the users. PA1 (3) the casing members B and C are connected together by weak connections D which may be broken easily if the casing members B and C are repeatedly opened and closed. PA1 (4) The opening of the casing members B and C requires certain complicated operation of the hooks and slots and thus causing an inconvenience to the users.
It is therefore desirable to provide a noise filtering device of the type described previously which removes the deficiencies of the prior art devices.